Although there are many colour micro-displays many of the prior art colour micro-displays have a number of disadvantages.
There is extensive literature reporting the development of micro-displays using technologies such as OLED, Liquid Crystal and MEMS. The latter two are based on pattern generators located externally to a light source that is permanently on full brightness, and consequently require extra components to form the micro-display. A further basic drawback then related to the power loss as all pixels must be addressed with light even if they are not used to display the image. The contrast ratio of such displays is also compromised.
OLED technology is an emissive technology and in simple terms is based on an anode and cathode surrounding a fluorescent emitting layer. These techniques often use white light with colour filters for small pixel formation. Consequently, approximately 60 to 70% of the spectral range of the white pixels are lost/not needed to achieve the colour gamut in a RGB display. In addition, white OLEDs are in themselves less efficient than monochrome OLEDs, such that in the end only 10 to 20% of the emitted light can actually be used. This does not take into account for the efficiencies of the overall OLED structure or how the light is extracted.
Moreover, the OLED structure is also more complex and involves electron transport layer, hole blocking layer and electron blocking layer all carefully controlled in thickness and refractive index. This is important for improved display performance as the electrically doped electron and hole transport layers enable enhanced charge injection and low operating voltages. The charge blocking layers help to confine charge carriers within the emission layer. Furthermore, other issues relate to the poor efficiencies and limited lifetimes in the blue OLED wavelength region and coupled with the low brightness levels mean that the display has fundamental limitations in performance.
Techniques do exist to provide surface mount bonding in individual LEDs. Typically, pick and place techniques can only be used for large LEDs. Thus limiting the pixels per inch for a display. It also means that there is the need for two electrical contacts per pixel. For the former point, techniques have been developed to pick and place micro-LEDs. However, to provide electrical contacts presents challenges for small pixel with post-processing required.
Disadvantages of such systems can be summarised by the following:                Manufacturing—time per flip-chip bond, simultaneous n and p connection for each pixel and ability to place pixels with <10 μm dimensions;        Post processing of pick and place micro-LEDs using semiconductor processing techniques. The provision of conformed contact layers across the LED arrays to form a secondary global contact. Or a combination of planarization techniques to provide a planarised structure on which a patterned contact layer is formed. The need to provide transparent contact layers for light escape or subsequent patterning of contact layers to enable this. The need to provide electrical connection to the control backplane.        Performance—in particular selection of green LED devices with small chromatic variation over drive current and temperature. Requirement to have each green LED emission wavelength in a tight distribution due to the eye's sensitivity to small variations in wavelengths near the peak of its visual response (i.e. green).        
It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
It is a further object of at least one aspect of the present invention to provide a low power consumption high brightness display and a method of manufacturing said display.